GCC generates the same code for 24kc and 34kc. Since we have
converted all 34kc targets to the 24kc, it's better to switch
kernel -mtune to 24kc to avoid confusing developers.
Signed-off-by: Shiji Yang <yangshiji66@outlook.com>
Link: https://github.com/openwrt/openwrt/pull/22703
Signed-off-by: Robert Marko <robimarko@gmail.com>